This invention relates generally to blow molds and more particularly to a parison closing or “pinch” apparatus having interchangeable actuation components.
In the process of blow molding, a parison which is similar to an empty balloon is inflated into the constraints of two mold halves. The parison is created as a continuous or interrupted extrusion. Some amount of air is continuously being blown into parison prior to closing the mold. The bottom section of the parison is sometimes closed prior to the mold closing over the parison. This allows the parison to be partially inflated prior to closure of the mold. After the mold is closed, the continuous or interrupted parison is effectively cut off into a single piece section. A common way to seal the lower end of the parison is to first introduce the parison into a space between the two mold halves when they are separated. Then two parison closing or “pinch” apparatus close upon the lower edge of the parison prior to the mold halves fully closing together. The closing apparatus may be provided as part of the mold, a separate assembly that is moved from machine to machine or is part of a blow mold machine.
The pinch apparatus is typically actuated by either springs or by a pneumatic cylinder. Using a spring actuated apparatus, pinch bars upon the pinch apparatus begin in an extended position and then sandwich the lower parison end as the mold starts to be closed. Then the pinch bars are pushed against each other and further retracted as the mold is brought together. The closing of the mold overcomes the force inherent in the springs. As the mold is opened, the springs force the pinch bars back into an extended position. In a version using a cylinder the cylinder pushes the pinch bar back into position, both directions (as opposed to only one direction with a spring) of motion of the pinch bar may be controlled. This can help optimize the partial inflation of the parison prior to the mold closing. However, often a particular mold can function with only one type of pinch apparatus. The pneumatic supply and control components which are part of the mold setup are often completely utilized by components of the mold itself. As a result no pneumatic components are available for the pinch apparatus. If the user does not own a spring actuated pinch apparatus, a completely new pinch apparatus must be purchased. A universal pinch apparatus is desired which may be quickly and easily retrofitted from spring actuation to cylinder actuation or vise versa without changing the other components of the pinch apparatus.